Heretofore, regarding this type of optical atmospheric link system, a system which can transmit data to and receive data from a remote target receiving/transmitting system by a light beam transmitted through space has been proposed (cf. Japanese Patent Application Lied Open No. 305734/1989).
As shown in FIG. 1, in the optical atmospheric link system, a laser diode LD is driven by a predetermined data signal and a light beam LA1 of a predetermined polarization plane is emitted from the laser diode LD.
A lens L1 collimates the light beam LA1 to a parallel luminous ray, which passes through polarization beam splitter 7, and via lenses L2 and L3 so as to be sent to the remote target system to be transmitted.
In this way, the optical atmospheric link system 1 delivers the light beam LA1 of a predetermined polarization plane to the remote target system to be transmitted.
The lens L3 receives the light beam arriving from the object of transmission, and then directs it to the polarization beam splitter 7 via the lens L2.
In the remote target system, a light beam LA2, which is orthogonal in the polarization plane to the light beam LA1, is transmitted to the optical atmospheric link system 1.
Hence, in the optical atmospheric link system 1, the light beam LA2 is reflected by the polarization splitter 7, and then condensed through a half mirror 8 and lens L4 to a light receiving element PD .
In this way, in the optical atmospheric link system 1, the light beam LA2 arriving from the remote target system is received so that the data can be received.
The light beam LA2 which arrives at the half mirror 8 is refracted through lens L5 to an incident position detecting element PSD, and the incident position is detected by a incident position detecting circuit 4. After the incident position detecting circuit 4 detects the incident position of the light beam LA2 by the incident position detecting element PSD, and then the difference from the desired incident position is sent to a drive circuit 5 as a deviation-voltage signal S.sub.DET.
The drive circuit 5 delivers a drive signal S.sub.DRV to an actuator 6 based on the deviation-voltage signal S.sub.DET so that the actuator 6 is driven, and thus the lens L2 is driven, and the incident position of the light beam LA2 is servo-controlled.
Similarly as shown in FIG. 2, the drive signal S.sub.DRV outputted from the drive circuit 5 is supplied to a motor M1 to turn a mirror barrel 2 up and down or right and left. Thus, the mirror barrel 2 is worked through a worm gear G1 fixed to the output axis of the motor M1 and a gear G2 set up on the mirror barrel 2. Therefore, the mirror barrel 2 is servo-controlled to turn up and down or right and left so that the incident position of the light beam LA2 can be controlled.
In the apparatus of FIG. 1, the path of the internal optical system is automatically shifted to the large-aperture lens L3 so as to match the path of light beam LA1 with the path of light beam LA2 in the atmospheric linking line. In this manner, because a small lens in the optical system is moved, the follow-up performance is comparatively high. However, the angle requirement (and the aberration) for the field of the optical system (the large-aperture lens L3) becomes greater, and there are problems of complexity of construction, for instance, by increasing of the number of the lenses.
Moreover, because the turning power of the motor M1 is transmitted to the mirror barrel 2 by a worm gear G1 and a gear G2, when the light axis of the optical atmospheric link system 1 is changed by disturbance, the changed must be corrected and servo-control in a short time is difficult.